Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
Case	Tag   Price	Sales   Tax %	Raw Total   Incl. Sales Tax	Rounded   to Penny	Rounded   to Nickel	Rounded   to Dime
Purchase #1	$177.33	6.558%	$188.9593	$188.96	$188.95	$189.00
Purchase #2	$192.82	6.763%	$205.8604	$205.86	$205.85	$205.90
Purchase #3	$142.38	10.637%	$157.525	$157.53	$157.55	$157.50
Purchase #4	$131.48	4.300%	$137.1336	$137.13	$137.15	$137.10
Purchase #5	$89.89	3.575%	$93.1036	$93.10	$93.10	$93.10
Purchase #6	$79.34	7.280%	$85.116	$85.12	$85.10	$85.10
Purchase #7	$226.48	11.761%	$253.1163	$253.12	$253.10	$253.10
7 purchase totals =	$1,039.72		$1,120.8142	$1,120.82	$1,120.80	$1,120.80